A number of dropping devices designed to produce distinct droplets are known. See for example U.S. Pat. Nos. 2,931,067; 3,208,101; 3,341,087 and 3,642,393. In each of these devices there is no bottom valve which controls the flow of liquid. The orifice restriction only restrains the liquid. U.S. Pat. No. 2,931,067 shows a pulsation which forces droplets of liquid through orifices in the bottom of the dropping device. U.S. Pat. No. 3,208,101, FIG. 6 shows how droplets can be formed using a bell and a ram to force droplets from an open tube. These devices are undesirable for preparing uniform droplets of a slurry at uniform time intervals.